According to the prior art, automatic drives, in particular for motor vehicles, comprise planetary gear sets, which are shifted by means of friction or, respectively, shift elements, such as clutches and brakes, and which are typically connected to a start-up element that is subject to a slip effect and that is optionally provided with a bypass clutch, such as a hydrodynamic torque converter or a hydraulic clutch.
Such an automatic drive is known from DE 199 12 480 84 by the Applicant, for example. This drive comprises three single-carrier planetary gear sets as well as three brakes and two clutches for the shifting of six forward gears and one reverse gear, an input drive shaft and an output shaft, wherein the carrier of the first planetary gear set is permanently connected to the ring gear of the second planetary gear set, and the carrier of the second planetary gear set is permanently connected to the ring gear of the third planetary gear set, and the input drive shaft is directly connected to the sun gear of the second planetary gear set.
In addition, in the known transmission, it is provided that the input drive shaft can be connected by means of the first clutch to the sun gear of the first planetary gear set, and can be connected by means of the second clutch to the carrier of the first planetary set, wherein the sun gear of the first planetary gear set can be connected by means of the first brake to a housing of the transmission, and the carrier of the first planetary gear set can be connected by means of the second brake to the housing of the transmission, wherein the sun gear of the third planetary gear set can be connected by means of the third brake to the housing of the transmission. The output shaft of the transmission is permanently connected to the carrier of the third planetary gear set and to the ring gear of the first planetary gear set.
In addition, a 9-speed multi-stage transmission is known from DE 29 36 969 A1; it comprises eight shift elements and four planetary gear sets, wherein a planetary gear set serves as a front mounted transmission and the main gearing has a Simpson set and a further planetary gear set which serves as a reverse gear.
Further multi-stage transmissions are known, for example from DE 10 2005 010 210 A1 and DE 10 2006 006 637 A1 by the Applicant.
Automatic vehicle transmissions in planetary design in general have already been described in the prior art and are subject to constant further development and improvement. These transmissions should have low construction costs, in particular a low number of shift elements, and with a sequential method of shifting, should avoid double shifting, i.e. a connection or, respectively, disconnection of two shift elements, so that when shifting in defined groups of gears, only one respective shift element is shifted.
A multi-stage transmission in planetary design is known from DE 10 2008 000 428 A1 by the Applicant, which has an input drive and an output drive, which is disposed in a housing. In the case of the known transmission, at least four planetary gear sets, referred to in the following as the first, second, third and fourth planetary gear set, at least eight rotatable shafts, referred to in the following as the input drive shaft, output shaft, third, fourth, fifth, sixth, seventh and eighth shaft, as well as at least six shift elements, comprising brakes and clutches, are provided, the selective meshing of which produces different transmission ratios between the input drive and the output drive, so that preferably nine forward gears and one reverse gear can be implemented.
The first and the second planetary gear sets, which are preferably designed as a minus planetary gear sets, this having a negative stationary transmission ratio, form a shiftable front mounted gear set thereby, wherein the third and the fourth planetary gear set form a main gear set.
In the case of the known multi-stage transmission, it is provided that the carriers of the first and of the second planetary gear set are coupled with one another by means of a fourth shaft, which is connected to an element of the main gear set, in that the ring gear of the first planetary gear set is coupled to the sun gear of the second planetary gear set by means of the eighth shaft, which can be detachably connected to the input drive shaft by means of a first clutch, and in that the sun gear of the first planetary gear set can be connected by means of a third shaft through a first brake to a housing of the transmission and can be detachably connected by means of a second clutch to the input drive shaft, wherein the ring gear of the second planetary gear set can be coupled by means of the fifth shaft through a second brake to a housing of the transmission. In addition, the seventh shaft is permanently connected to at least one element of the main gear set and can be connected by means of a third brake to the housing of the transmission, wherein the sixth shaft is permanently connected to at least one additional element of the main gear set and is detachably connected by means of a third clutch to the input drive shaft; the output shaft is permanently connected to at least one additional element of the main gear set.
In the known transmission, the fourth shaft is preferably permanently connected to the ring gear of the third planetary gear set, wherein the sixth shaft is permanently connected to the ring gear of the fourth planetary gear set and to the carrier of the third planetary gear set, and can be detachably connected by means of the third clutch to the input drive shaft. In addition, the seventh shaft is permanently connected to the sun gears of the third and fourth planetary gear set, and can be connected by means of the third brake to a housing of the transmission. The output drive is produced thereby by means of the output shaft, which is permanently connected to the carrier of the fourth planetary gear set. In addition, the third and the fourth planetary gear set can be assembled or, respectively, reduced into a Ravigneaux gear set having a common carrier and a common ring gear.